Heat-Treated Sapphires: What It Means, Why It’s Common, and When It Matters It’s common to feel a moment of hesitation when you see “heat treated” on a sapphire listing. In reality, heat treatment is one of the most established and widely accepted practices in the sapphire world, provided it is disclosed clearly. We stock many heat-treated sapphires, and we’re comfortable recommending them. Some of the most beautiful and high-value sapphires we’ve sourced and sold have been heat treated. What matters is how the stone performs, how it was disclosed, and whether it suits the piece you’re creating. What is heat treatment in sapphire? Heat treatment is the controlled heating of corundum (ruby and sapphire) to improve colour and or clarity. Often, the goal is to reduce the appearance of “silk” and other fine inclusions that can make a stone look hazy, and to allow the colour to present more cleanly. How common is heat treatment? There isn’t one single official percentage published by major labs that applies to every deposit and every quality tier. However, across the commercial sapphire market, trade estimates frequently sit around 90 to 95% being heat treated in some form. Treat it as a rule of thumb, not a promise. The practical takeaway is simple. Unheated sapphire is the rarity, and rarity is part of why it can command a premium when confirmed by an independent lab. Is heat treatment stable? Yes. Standard heat treatment is considered stable under normal wear. From a care standpoint, heat-treated sapphire is generally treated as durable and suitable for everyday jewellery. Does heat treatment affect value? Sometimes, but it’s rarely as simple as “treated is lesser”. Untreated sapphires can be rarer, which is why they may command a premium when that status is supported by independent verification. On the other hand, a heat-treated sapphire can still be exceptional, and priced accordingly, because the beauty is there. A simple way to think about it: If you’re buying primarily for rarity and collectability, you may decide to prioritise untreated. If you’re buying to wear and love, heat treatment alone is not a reason to dismiss a sapphire. How hot are sapphires heated? It depends on the material and the outcome being targeted, but classic gemmology references commonly describe high-temperature heating in the range of roughly 1500°C to 1700°C for corundum when the goal is to dissolve rutile silk and improve clarity. This is well below sapphire’s melting point, and it’s done in controlled furnaces, not at the jeweller’s bench. What actually changes inside the stone? The inclusion clients hear about most often is rutile silk, fine needle-like inclusions that can create a soft haze or a sleepy look. Under sufficient heat, rutile can dissolve back into the sapphire, improving transparency and often making colour look cleaner and more saturated. Heating can also alter other micro-inclusions and internal features depending on their chemistry, which is why labs look for a combination of signs rather than relying on one single “tell”. How we source sapphires, and why disclosure matters We source from local and overseas miners and gemstone cutters who disclose treatments as part of responsible supply. When treatment status meaningfully affects the decision or the price, we can provide independent certification so you’re not relying on assumptions or marketing language. This is where sapphire buying becomes much simpler. Rather than fixating on a single label, you can look at the full picture: colour, transparency, cut, durability, and documentation. Curious what heat-treated sapphires can look like when they’re chosen well? Start by browsing our Gem Vault, then if you’d like guidance or a custom cut, send through a bespoke enquiry. Shop the Gem Vault Make a Bespoke Enquiry Book an Appointment Gemstone Shape Guide Contact Us
